The Electrophilic Character of Bunsen's Cacodyl Disulfide, Me₂As(S)‐S‐AsMe₂

Abstract

The behaviour of Bunsen's cacodyl disulfide, Me 2 As(S)-S-AsMe 2 towards Lewis bases of group 15 of the Periodic Table was studied mainly by 1 H NMR. While Ph 3 N did not react, 4dimethylaminopyridine and triethylamine isomerized the disulfide to Me 2 AsSSAsMe 2 . Ph 3 P, (PhO) 3 P, (MeO) 3 P, (EtO) 3 P and Ph 3 As desulfurized the disulfide to Me 2 AsSAsMe 2 . (PhS) 3 P also desulfurized the disulfide but Me 2 As-S-SPh was also produced. Me 2 As-S-SPh was the main product with (PhS) 3 As nucleophile. In most sys-2077 tems, cationic and anionic species were formed. The results are best interpreted by initial attack of the nucleophile on the electrophilic AsϭS sulfur.

The Lewis-base behavior of Bunsen's cacodyl disulfide, Me2As(S)‒S‒AsMe2, toward molecular halides of group 13

“…The eluate, however, contained 2 (*95%) and 1 (*5%), implying that free 1 was thermodynamically unstable, reverting back to equilibrated 2 þ 1 [3]. On the TLCs we detected S 8 , as well, coming from the decomposition of 2 on silica gel [4]. That 1 is thermodynamically unstable was alluded to earlier where the reaction of Me 2 AsÀ ÀI with Na 2 S 2 gave 2 and not 1 [3].…”

“…4-dimethylaminopyridine or Et 3 N, on 2 where fission, e.g. to Me 2 AsÀ ÀSÀ ÀNR 3 þ and Me 2 AsÀ ÀS 7 , and recombination leads to increased amounts of 1 [4]. Therefore, the isomerization of 2 to 1 by BF 3 Á Et 2 O and by AlCl 3 can proceed either intermolecularly (after splitting and recombination of the fragments) or intramolecularly, Scheme 1.…”

“…The eluate was evaporated and dried to give a solid and traces of oil (50.2 mg). By TLC (Et 2 O/peth 1:1) it contained either 1 or Me 2 AsÀ ÀSÀ ÀAsMe 2 3 and S 8 [4]. By 1 H NMR (CDCl 3 , TMS) it contained 2 and 1 (1:0.05 molecule/molecule) very close to the self equilibrated 2 1 [3].…”

“…Ph 3 P, (RO) 3 P, (PhS) 3 P giving the desulfurized product Me 2 AsÀ ÀSÀ ÀAsMe 2 3, Equation (2), with Et 3 N or 4-dimethylaminopyridine gives increased amounts of the isomerized product 1, and with (PhS) 3 As gives Me 2 AsÀ ÀSÀ ÀSPh 4 and other compounds, Equation (3) [4].…”

“…The electrophilic atom in 2 is the As¼S sulfur [4]. Bunsen found that 2 reacted with heavy metal cations, e.g.…”